Fender75 Power Switch

[Gingertube]

I had a call from my friend , he's bring me his Fender 75 to have the power switch replaced, this will be the 3rd time in 18 months.

The switches have been welding contacts such that the amp stays on when turned off.

Is there a higher current rated switch available that might last longer than the 3A rated jobs I have been putting in?

Is it worth trying the 10nF ceramic cap across the contacts trick to see if that improves the liftime?

I have some 16A rated switches which match asthetically but just will not fit (not enough behind the panel space).

Any suggestions?

Thanks,
Ian

[Enzo]

Was the original switch only rated at 3A 240vAC? That is a very low current rating for a full size toggle switch. Since the amp is over 30 years old, how long did the original switch last, most of that time? I worry when a failing part becomes a re-engineering project.

I would normally suggest checking the current draw through the mains, but if you are mounting 3A switches on an amp with a 3A fuse, I don't doubt they freeze up.

I'd be looking through more options from suppliers.

But if you must modify the thing, a couple thoughts:
You could add an inrush limiting thermistor as Fender has done on a number of amps. Wired in series with the mains, somewhere between the mains fuse and the voltage selector switch. A Fender Hot Rod DeVille is an example of this.

You could wire a power triac in place of the power switch, and then wire the switch to control the gate of the triac. That way the switch only carries the tiny gate current of the triac, the triac does the switching. A Peavey CS800 uses this arrangement as an example that comes to mind, or a Peavey Renown400.

[pdf64]

Yes, I'm a big fan of inrush current limiters.
My Fender 75 used to pop the occasional T3A fuse but since fitting the limiter about a decade ago, I can't remember the last time the T2A I replaced it with popped.
Prior to that, I had replaced the power switch with a 6A type.
Pete

[Gingertube]

Thanks guys,
As luck would have it, I have some 3 Amp rated Inrush Current Limiters left over from the day job (I used 2 in series to limit peak inrush current in an aircraft mounted laser power supply). Not sure why I had'nt thought of putting one in before - there sometimes seems to be a disconnect between what I do in the Design Eng day job and what I do in the hobby tube amp design/build/repair/restore jobs, and there really should not be, after all, electricity is electricity. Maybe the onset of senility, I'll have to whatch out for that, if I remember.
Cheers,
Ian